Edge seal for lower electrode assembly

ABSTRACT

A lower electrode assembly useful for supporting a semiconductor substrate in a plasma processing chamber includes a temperature controlled lower base plate, an upper plate, a mounting groove surrounding a bond layer and an edge seal comprising an elastomeric band having an outer concave surface in an uncompressed state, the band mounted in the groove such that upper and lower ends of the band are axially compressed and a maximum outward bulging of the band is no greater than a predetermined distance.

FIELD OF THE INVENTION

The present disclosure relates to improvements in edge seals for lowerelectrode assemblies used in plasma processing chambers such as plasmaetch reactors.

BACKGROUND

Integrated semiconductor circuits have become the primary components ofmost electronics systems. These miniature electronic devices may containthousands of the transistors and other circuits that make up the memoryand logic subsystems of microcomputer central processing units and otherintegrated circuits. The low cost, high reliability and speed of thesecircuits have led them to become a ubiquitous feature of modem digitalelectronics.

The fabrication of integrated semiconductor circuits typically takesplace in a reactive ion etching system, such as a parallel plate reactoror inductively coupled plasma reactor. A reactive ion etching system mayconsist of an etching chamber with an upper electrode or anode and alower electrode or cathode positioned therein. The cathode is negativelybiased with respect to the anode and the container walls. The wafer tobe etched is covered by a suitable mask and placed directly on thecathode. A chemically reactive gas such as CF₄, CHF₃, CClF₃, HBr, Cl₂and SF₆ or mixtures thereof with O₂, N₂, He or Ar is introduced into theetching chamber and maintained at a pressure which is typically in themillitorr range. The upper electrode is provided with gas hole(s) whichpermit the gas to be uniformly dispersed through the electrode into thechamber. The electric field established between the anode and thecathode will dissociate the reactive gas forming plasma. The surface ofthe wafer is etched by chemical interaction with the active ions and bymomentum transfer of the ions striking the surface of the wafer. Theelectric field created by the electrodes will attract the ions to thecathode, causing the ions to strike the surface in a predominantlyvertical direction so that the process produces well-defined verticallyetched side walls.

SUMMARY

A lower electrode assembly useful for supporting a semiconductorsubstrate in a plasma processing chamber comprises an upper plate, atemperature controlled lower base plate, a mounting groove surrounding abond layer in the lower electrode assembly, and an edge seal comprisingan elastomeric band having an outer concave surface in an uncompressedstate, the band mounted in the groove such that upper and lower ends ofthe band are axially compressed and a maximum outward bulging of theband is no greater than a predetermined distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a processing chamber suitable forplasma etching semiconductor substrates.

FIG. 2 shows a cross-sectional view of an upper ceramic layer and lowerbase plate of an electrode assembly having a mounting groovetherebetween.

FIG. 3 shows a cross-sectional view of a rectangular elastomeric banddisposed in the mounting groove between an upper ceramic layer and lowerbase plate of an electrode assembly.

FIG. 4 shows a cross-sectional view of an elastomeric band having aconcave outer surface fitted in the mounting groove between an upperceramic layer and lower base plate of an electrode assembly.

FIG. 5 shows a cross-sectional view of an elastomeric band having aconcave outer surface in an uncompressed state.

FIG. 6 shows a cross-sectional view of an elastomeric band having aconcave outer surface under compression such that the degree ofcompression in an axial direction is ten to fifteen percent.

FIG. 7 shows a cross-sectional view of an elastomeric band having aninclined outer surface fitted in the mounting groove between an upperceramic layer and lower base plate of an electrode assembly.

FIG. 8 shows a cross-sectional view of an elastomeric band having a pairof outer converging surfaces fitted in a mounting groove between anupper ceramic layer and lower base plate of an electrode assembly.

DETAILED DESCRIPTION

A lower electrode assembly typically includes an electrostatic clampinglayer on which a wafer is clamped during processing in a plasmaprocessing chamber. The lower electrode assembly can also includevarious layers bonded to a temperature controlled base plate. Forexample, the assembly can include an upper ceramic layer incorporatingone or more electrostatic electrodes adhesively bonded to an upper sideof a heater plate, one or more heaters adhesively bonded to a bottom ofthe heater plate, and a base plate adhesively bonded to the heaters andheater plate. To protect the exposed adhesive bond layers, the heaterplate has a smaller diameter than the ceramic layer and base plate andan edge seal of elastomeric material is located in a mounting groovebetween the ceramic layer and the base plate. To provide an effectiveseal, the edge seal is axially compressed 1 to 20%, preferably about 5%to completely fill the mounting groove. For an edge seal in the form ofa ring with a rectangular cross section, such compression causes theouter surface of the seal to bulge outwardly and such outward expansioncould contact a surrounding edge ring. To address this problem, the edgeseal is configured to account for changes in dimensions due to radialexpansion.

To protect the bond layers, the edge seal can comprise an elastomericband with a concave outer surface whereby axial compression of the bandwhen mounted in the mounting groove does not cause expansion of theband's outer surface beyond a predetermined distance such as the maximumouter diameter of the band in an uncompressed state. The elastomericband is designed to fit in a rectangular mounting groove such that theelastomeric band is constrained on three sides, with the fourth sidebeing unconstrained and exposed to reactive chamber conditions, therebyprotecting the bond layers.

FIG. 1 shows a cross-sectional view of an exemplary plasma reactor 10for etching substrates. As shown in FIG. 1, the plasma reactor 10includes a plasma processing chamber 12, an antenna disposed above thechamber 12 to generate plasma, which is implemented by a planar coil 16.The RF coil 16 is typically energized by an RF generator 18 via amatching network (not shown). Such chambers are called inductivelycoupled plasma (ICP) chambers. To supply process gas to the interior ofthe chamber 12, there is provided a gas distribution plate or showerhead14, which preferably includes a plurality of holes for releasing gaseoussource materials, e.g., the etchant source gases, into the RF-inducedplasma region between the showerhead 14 and a semiconductor substrate orwafer 30 supported on a lower electrode assembly 28. While aninductively coupled plasma reactor is shown in FIG. 1, the plasmareactor 10 can incorporate other plasma generating sources such ascapacitive coupled plasma (CCP), microwave, magnetron, helicon, or othersuitable plasma generating equipment, in which case the antenna isomitted.

The gaseous source materials may also be introduced into the chamber 12by other arrangements such as one or more gas injectors extendingthrough the top wall and/or gas ejection ports built into the walls ofchamber 12. Etchant source chemicals include, for example, halogens suchas Cl₂ and BCl₃ when etching through aluminum or one of its alloys.Other etchant chemicals (e.g., CH₄, HBr, HCl, CHCl₃) as well as polymerforming species such as hydrocarbons, fluorocarbons, andhydro-fluorocarbons for side-wall passivation of etched features mayalso be used. These gases may be employed along with optional inertand/or nonreactive gases.

In use, a wafer 30 is introduced into chamber 12 defined by chamberwalls 32 and disposed on the lower electrode assembly 28. The wafer 30is preferably biased by a radio frequency generator 24 (also typicallyvia a matching network). The wafer 30 can comprise a plurality ofintegrated circuits (ICs) fabricated thereon. The ICs, for example, caninclude logic devices such as PLAs, FPGAs and ASICs or memory devicessuch as random access memories (RAMs), dynamic RAMs (DRAMs), synchronousDRAMs (SDRAMs), or read only memories (ROMs). When the RF power isapplied, reactive species (formed from the source gas) etch exposedsurfaces of the wafer 30. The by-products, which may be volatile, arethen exhausted through an exit port 26. After processing is complete,the wafer 30 can be subjected to further processing and eventually dicedto separate the ICs into individual chips.

The plasma exposed surfaces of any plasma confinement apparatus (notshown), chamber wall 32, chamber liner (not shown) and/or showerhead 14can be provided with a plasma sprayed coating 20 with surface roughnesscharacteristics that promote polymer adhesion. In addition, plasmaexposed surfaces of the substrate support 28 can also be provided with aplasma sprayed coating (not shown). In this manner, substantially allsurfaces that confine the plasma will have surface roughnesscharacteristics that promote polymer adhesion. In this manner,particulate contamination inside the reactor can be substantiallyreduced.

It can be appreciated that the reactor 10 can also be used for metal,dielectric and other etch processes. In plasma etch processing, the gasdistribution plate can be a circular plate situated directly below adielectric window in an ICP reactor or form part of an upper electrodeassembly in a CCP reactor called a parallel plate reactor wherein thegas distribution plate is a showerhead electrode oriented parallel to asemiconductor substrate or wafer 30. The gas distributionplate/showerhead electrode contains an array of holes of a specifieddiameter and spatial distribution to optimize etch uniformity of thelayers to be etched, e.g., a photoresist layer, a silicon dioxide layerand an underlayer material on the wafer.

An exemplary parallel-plate plasma reactor that can be used is adual-frequency plasma etch reactor (see, e.g., commonly-owned U.S. Pat.No. 6,090,304, which is hereby incorporated by reference in itsentirety). In such reactors, etching gas can be supplied to a showerheadelectrode from a gas supply and plasma can be generated in the reactorby supplying RF energy at different frequencies from two RF sources tothe showerhead electrode and/or a bottom electrode. Alternatively, theshowerhead electrode can be electrically grounded and RF energy at twodifferent frequencies can be supplied to the bottom electrode.

FIG. 2 shows a cross-sectional view of a lower electrode assembly 150having various layers bonded together with exposed bond layers locatedin a mounting groove adapted to receive an edge seal comprising anelastomeric band. The electrode assembly 150 comprises an upper ceramicmember 180 incorporating an electrostatic clamping electrode andattached to a lower member 100 such as a temperature controlled baseplate. Disposed between the upper member 180 and the lower member 100 isa heater plate 140 comprising a metal or ceramic plate and one or moreheaters such as a film heater coupled to the bottom of the plate.Adhesive bonding layer 120 is disposed between the lower member 100 andthe heater plate 140 and bonds lower member 100 to heater plate 140.Adhesive bonding layer 160 is disposed between the upper member 180 andthe heater plate 140 and bonds upper member 180 to heater plate 140. Theupper member 180 and lower member 100 extend beyond the heater plate 140and bonding layers 120, 160 to form an annular groove 190. The outerperipheries 145, 125, 165 of the heater plate 140 and bond layers 120,160 are substantially aligned with respect to one another. The outerperipheries 185, 105 of the upper member 180 and lower member 100 may ormay not be vertically aligned and additional layers may be includedbetween the upper and lower members.

The upper member 180 preferably is an electrostatic clamping layer ofceramic material and embedded electrode comprised of a metallicmaterial, such as W, Mo etc. In addition, the upper member 180preferably has a uniform thickness from the center to the outer edge ordiameter thereof. The upper member 180 is preferably a thin circularplate suitable for supporting 200 mm, 300 mm or 450 mm diameter wafers.Details of a lower electrode assembly having an upper electrostaticclamping layer, heater layer and bonding layers are disclosed incommonly owned U.S. Published Patent Application 2006/0144516 whereinthe upper electrostatic clamping layer has a thickness of about 0.04inch, the upper bonding layer has a thickness of about 0.004 inch, theheater plate comprises a metal or ceramic plate of about 0.04 inchthickness and a heater film of about 0.01 inch thickness, and the lowerbonding layer has a thickness of about 0.013 to 0.04 inch. Therectangular mounting groove between the upper clamping layer and thebase plate has a height of at least about 0.05 to 0.09 inch and a widthof about 0.035 inch. In a preferred embodiment for processing 300 mmwafers, the groove can have a height of at least about 0.07 inch and awidth of about 0.035 inch. When inserted in the groove, the edge seal ispreferably expanded radially and compressed vertically to tightly fit inthe groove. However, if the edge seal has a rectangular cross section itwill bulge outwardly and may contact a surrounding edge ring and/ortensile stresses on the outer surface of the edge seal can lead tocracking when exposed to fluorine or oxygen plasmas.

The lower base plate 100 is preferably a circular plate having an uppersurface and lower surface. In one embodiment, the lower member 100 canbe configured to provide temperature control by the inclusion of fluidchannels (not shown) therein through which a temperature controlledliquid can be circulated to the electrode assembly 150. In an electrodeassembly 150, the lower member 100 is typically a metal base plate whichfunctions as the lower RF electrode in the plasma chamber. The lowermember 100 preferably comprises an anodized aluminum or aluminum alloy.However, it can be appreciated that any suitable material, includingmetallic, ceramic, electrically conductive and dielectric materials canbe used. In one embodiment, the lower member 100 is formed from ananodized machined aluminum block. Alternatively, the lower member 100could be of ceramic material with one or more electrodes located thereinand/or on an upper surface thereof.

As shown in FIG. 2, bond layer 120 bonds the lower member 100 to theheater plate 140. Bond layer 160 bonds the upper member 180 to theheater plate 140. The bond layers 120, 160 are preferably formed from alow modulus material such as an elastomeric silicone or silicone rubbermaterial. However, any suitable bonding material can be used. It can beappreciated that the thickness of the bond layers 120, 160 can varydepending on the desired heat transfer coefficient. Thus, the thicknessthereof is adapted to provide a desired heat transfer coefficient basedon manufacturing tolerances of the bond layers. Typically, the bondlayers 120, 160 will vary over its applied area by plus or minus aspecified variable. Typically, if the bond layer thickness does not varyby more than 1.5 percent, the heat transfer coefficient between theupper and lower members 180, 100 can be made substantially uniform.

For example, for an electrode assembly 150 used in the semiconductorindustry, the bond layers 120, 160 preferably have a chemical structurethat can withstand a wide range of temperatures. Thus, it can beappreciated that the low modulus material can comprise any suitablematerial, such as a polymeric material compatible with a vacuumenvironment and resistant to thermal degradation at high temperatures(e.g., up to 500° C.). In one embodiment, bond layers 120, 160 maycomprise silicone and be between about 0.001 to about 0.050 of an inchthick and more preferably about 0.003 to about 0.030 of an inch thick.

The heater plate 140 can comprise a laminate bonded to a lower surfaceof the upper member 180. For example, heater plate 140 can be in theform of a metal or ceramic plate with a film heater coupled to a bottomof the metal or ceramic plate. The heater film can be a foil laminate(not shown) comprising a first insulation layer (e.g., dielectriclayer), a heating layer (e.g., one or more strips of electricallyresistive material) and a second insulation layer (e.g., dielectriclayer). The insulation layers preferably consist of materials having theability to maintain its physical, electrical and mechanical propertiesover a wide temperature range including resistance to corrosive gases ina plasma environment such as Kapton or other suitable polyimide films.The heater element(s) preferably consists of a high strength alloy suchas Inconel or other suitable alloy or anti-corrosion and resistiveheating materials. Typically, the film heater is in the form of alaminate of Kapton, Inconel and Kapton having a total thickness of about0.005 to about 0.009 of an inch and more preferably about 0.007 of aninch thick.

As shown in FIG. 2, outer peripheries 105, 185 of the lower member 100and upper member 180 can extend beyond the outer peripheries 145, 125,165 of the heater plate 140 and bond layers 120, 160, thereby forming amounting groove 190 in the electrode assembly 150. The material(s) ofbond layers 120, 160 are typically not resistant to the reactive etchingchemistry of semi-conductor plasma processing reactors and must,therefore, be protected to accomplish a useful operation lifetime. Toprotect the bond layers 120, 160, it has been proposed to place an edgeseal in the form of an elastomeric band into groove 190 to form a tightseal that prevents penetration of the corrosive gases of semi-conductorplasma processing reactors. See, for example, commonly owned U.S.Published Applications 2009/0290145 and 2010/0078899.

FIG. 3. shows a cross-sectional profile of an electrode assembly 150that includes an annular elastomeric band 200 with a rectangularcross-sectional profile. When the band 200 is disposed in groove 190,the band 200 is axially compressed such that its inner wall bulges awayfrom the outer surface of the heater plate 140 and its outer wallbecomes convex in shape. To accommodate for the larger diameter of theband, a surrounding edge ring would need to have its inner diameterexpanded or the parts would contact each other and rubbing due tothermal cycling could lead to particle generation in the chamber. Toaddress this problem, the band can be modified to have a shape whichavoids undesired bulging when axially compressed in the groove.

FIG. 4 shows a cross-sectional view of an electrode assembly 150 andmodified edge seal comprising elastomeric band 200. The electrodeassembly 150 of FIG. 4. is the same as the electrode assembly of FIG. 2and FIG. 3 but the band 200 has a concave outer surface to reducebulging when the band is axially compressed in the groove 190. As usedherein “concave” means that the outer surface does not have a uniformdiameter and instead has a depressed surface formed by one on morecurved or inclined surfaces along all or part of the outer surface. Theinner surface can have a uniform diameter or the inner surface can alsobe a concave surface. The outer surface can include one or morecylindrical sections of uniform diameter at the upper and/or lower endsof the band.

The elastomeric band 200 can be constructed from any suitablesemiconductor processing compatible material. For example, curablefluoroelastomeric fluoropolymers (FKM) capable of being cured to form afluoroelastomer or curable perfluoroelastomeric perfluoropolymers (FFKM)can be used. The elastomeric band 200 is preferably constructed of apolymer such as a fluorocarbon polymer material such as Teflon(PTFE—PolyTetraFluoroEthylene, manufactured by DuPont). However,plastics, polymeric materials, Perfluoroalkoxy (PFA), fluorinatedpolymers, and polyimides can be used. The elastomeric band 200 ispreferably comprised of a material having high chemical resistance, lowand high temperature capability, resistance to plasma erosion in aplasma reactor, low friction, and electrical and thermal insulationproperties. A preferred material is a perfluoroelastomer having a ShoreA hardness of 60 to 75 and a specific gravity of 1.9 to 2.1 such asPERLAST available from Perlast Ltd. Another band material is KALREZavailable form DuPont Performance Elastomers. PERLAST and KALREZ areFFKM elastomers.

FIG. 5 shows a cross-sectional view of an elastomeric band 200 in anon-compressed state prior to placement in the groove 190. Thedimensions of the elastomeric band 200 are not particularly limited, aslong as the dimensions are able to form, or adapt to form, a tight sealin a mounting groove of an electrode assembly such that an outward bulgeis minimized, if not eliminated. Preferably, the band geometry isdesigned to accommodate up to 20% axial compression preferably 1-10%axial compression and minimize outward bulging of the band beyond itsmaximum outer diameter in the uncompressed state. For a substratesupport designed to support a 200 or 300 mm wafer, the maximum outwardbulging due to axial compression is preferably 0.004 inch, morepreferably 0.002 inch. In an embodiment, the band includes an innercylindrical surface of uniform diameter, a flat annular upper surface, aflat annular lower surface smaller in width than the upper surface, anda concave outer surface. In a preferred embodiment, the band can have aheight of about 0.131 inch and maximum width of about 0.035 inch, theouter surface including an upper cylindrical section of uniform diameterextending vertically about 0.01 inch from the upper surface and a curvedsurface having a radius of about 0.35 inch extending from the uppercylindrical surface and an optional lower cylindrical surface extendingvertically from the lower surface. Each corner of the band is preferablyrounded with a radius of 0.002 to 0.01 inch, For other groove sizes, theheight 214 of the elastomeric band 200 is not particularly limited andcan be between about 0.05 to about 0.15 inches. The width 213 of theelastomeric band 200 is not particularly limited and can be betweenabout 0.02 to about 0.10 inches, e.g., 0.025 to 0.050 inch. Dimension211 is the depth of concavity of elastomeric band 200. This dimension isnot particularly limited and can be between about 0.001 to about 0.010inches. Dimension 212 is an optional flat portion of the elastomericband 200 in accordance with the present invention, as the concavity doesnot have to be extend the entire height 214 of elastomeric band 200. Theoptional upper flat portion may contribute to decreasing the erosionrate of the elastomeric band 200, as well as the bonding layers 120, 160protected by the elastomeric band 200. Dimension 212 can be from about0.01 to about 0.1 inches. The concavity of the elastomeric band 200 canhave a radius of curvature from about 0.2 to about 0.8 inches or beformed by one or more inclined surfaces.

The elastomeric band 200 of FIG. 6 is shown in a compressed state (e.g.,inserted into a groove of an electrode assembly). The compressed staterefers to the compression of the height 214 of elastomeric band 200 wheninserted into a groove of an electrode assembly. Typical compression isgenerally between 1%-20% and more specifically, between 1-10%, and mostpreferably about 5%. In other words, if the height 214 of elastomericband 200 is 1.0 inch when uncompressed, a 10% compression results inelastomeric band 200 having a height 214 of 0.9 inches. Dimension 215 isa predetermined distance corresponding to the allowable bulgingtolerance of elastomeric band 200 under a given compression rate. Undercompression, the elastomeric band 200 may retain it's concavecharacteristics, as denoted by the dotted line of 218, or the band 200may not retain it's concave characteristics, as denoted by the solidline of 218. However, the band may bulge beyond line 218 provided theextent of the bulging is not so much that the band contacts asurrounding edge ring. As an example, dimension 215 can be set such thatthe allowable bulge tolerance does not allow for the elastomeric band200 to significantly extend beyond the outer peripheries 185, 105 of theupper member 180 and lower member 100. Dimension 215 can be betweenabout 0.001 to about 0.01 inches, and is preferably less than about0.004 inches. Dimension 215 can be limited to less than 0.004 inches ifoptional cylindrical section 212 (shown in FIG. 5) is included at thetop of the band and is about 0.01 inches in height, with the remainderof the outer surface having a radius of curvature 216 of about 0.35inch. A preferred aspect ratio of height:thickness of the band is 2 to5.

Methods of making an electrode assembly 150 with an elastomeric band 200are not particularly limited and may comprise heating the band to expandit and pressing the heated band in the groove between the upper andlower members. In an alternative method, the band is expanded and fittedaround the heater plate prior to bonding the upper member to the heaterplate. In use, the band protects the bonding layers during processing ofa wafer supported on the upper member.

FIG. 7 shows a cross-sectional view of an elastomeric band 200 inaccordance with another embodiment wherein the outer surface of theelastomeric band is an inclined surface oriented such that the band iswider at its upper end.

FIG. 8 shows a cross-sectional view of an elastomeric band 200 whereinthe outer surface of the elastomeric band comprises two convergingsurfaces that form an angle that is less than 180° with respect to eachother. For example, the angle formed by the two surfaces may be 110 to140°, preferably about 120°.

In a preferred embodiment, the electrode assembly 150 is anelectrostatic chuck (ESC) useful for clamping substrates such assemiconductor wafers during processing thereof in a vacuum processingchamber for semiconductor fabrication, e.g., a plasma reactor such as aplasma etch reactor. The ESC can be a mono-polar or a bi-polar design.The electrode assembly 150, however, can be used for other purposes suchas clamping substrates during chemical vapor deposition, sputtering, ionimplantation, resist stripping, etc.

It can be appreciated that the electrode assembly 150 can be installedin any new processing chamber suitable for plasma processingsemiconductor substrates or used to retrofit existing processingchambers. It should be appreciated that in a specific system, thespecific shape of the upper member 180, the lower member 100 and theheater 140 may vary depending on the arrangement of chuck, substrateand/or other components. Therefore, the exact shape of the upper member180, the lower member 100 and the heater 140 as shown in FIGS. 2-8 areshown for illustration purposes only and are not limiting in any way.

The edge seal can be mounted in other lower electrode assemblies whichdo not include heater plates. For example, the elastomeric band can bemounted in a mounting groove surrounding a bond layer in a lowerelectrode assembly having an upper plate, and a temperature controlledlower base plate wherein the band is mounted in the groove such thatupper and lower ends of the band are compressed and a maximum outwardbuilding of the band is no greater than a predetermined distance.

An edge seal as disclosed herein can provide advantages over elastomericbands with rectangular cross-sections. For example, the edge seal withconcave outer surface can provide increased serviceability of the lowerelectrode assembly in chambers such as plasma etch chambers. Thisincreased serviceability results from a reduced tendency of the outersurface to crack when the edge seal is axially compressed in themounting groove and less tendency to bind with surrounding parts such asedge rings. If desired, the band can include a geometrical feature onits inner surface such as one or more grooves or projections such asdimples. Such features provide a ready indicator of which surface shouldface the groove when the band is installed in a groove.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described can be made without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A lower electrode assembly useful for supportinga semiconductor substrate in a plasma processing chamber comprising: atemperature controlled lower base plate, an upper plate, and a mountinggroove surrounding a bond layer in the lower electrode assembly; and anedge seal comprising an elastomeric band having an outer concave surfacein an uncompressed state, the band mounted in the groove such that upperand lower ends of the band are axially compressed and a maximum outwardbulging of the band is no greater than a predetermined distance.
 2. Theelectrode assembly of claim 1, wherein the concave surface is a singlecurved surface, a single inclined surface oriented such that the band iswidest at an upper end thereof and narrowest at a lower end thereof or apair of converging inclined surfaces oriented such that the band iswidest at upper and lower ends thereof and narrowest at a middlethereof.
 3. The electrode assembly of claim 1, wherein the outer surfaceof the band includes a cylindrical surface of uniform diameter at anupper end of the band extending less than 1/10 of the height of theband.
 4. The electrode assembly of claim 1, wherein the band has aheight of 0.05 to 0.15 inch, a width of 0.025 to 0.040 inch, and innerdiameter of 11.3 to 11.4 inches and each edge of the band is roundedwith a radius of 0.001 to 0.010 inch.
 5. The electrode assembly of claim1, wherein the band has an upper annular surface, a lower annularsurface smaller in width than the upper annular surface, a cylindricalinner surface of uniform diameter extending between the upper and lowerannular surfaces, an outer cylindrical surface of uniform diameterextending about 0.01 inch from the upper annular surface and a curvedsurface of uniform radius extending between the outer cylindricalsurface and the lower annular surface.
 6. The electrode assembly ofclaim 1, wherein the upper layer comprises a ceramic material having atleast one electrostatic clamping electrode embedded therein.
 7. Theelectrode assembly of claim 1, wherein the lower plate is an aluminumbase plate having fluid channels therein through which coolant iscirculated for maintaining the base plate at a constant temperature. 8.The electrode assembly of claim 1, wherein the predetermined distance isno greater than 0.004 inch and/or the band is axially compressed 1 to20%.
 9. The electrode assembly of claim 1, wherein the lower electrodeassembly further comprises a heater plate comprising a metal or ceramicplate having one or more spatially distributed heaters and the bondlayer comprises a first bond layer attaching the lower plate to theheater plate and a second bond layer attaching the heater plate to theupper plate, the mounting groove formed by an outer surface of theheater plate and opposed surfaces of the upper and lower plates.
 10. Theelectrode assembly of claim 1, wherein the band includes a cylindricalinner surface of uniform diameter, flat upper and lower surfaces ofequal width, an outer curved surface extending between the upper andlower surfaces, and each edge of the band is rounded.
 11. A plasma etchchamber wherein the electrode assembly of claim 1 is mounted in aninterior thereof and the upper layer of the electrode assembly includesan electrostatic chuck (ESC).
 12. A method of making the electrodeassembly of claim 1, comprising pressing the band into the groove suchthat the band is axially compressed at least 1%.
 13. An edge, seal for alower electrode assembly useful for supporting a semiconductor substratein a plasma processing chamber wherein the lower electrode assemblyincludes a temperature controlled lower base plate, a heater plate, anupper plate, a first bond layer attaching the lower plate to the heaterplate, a second bond layer attaching the heater plate to the upper plateand a mounting groove formed by an outer surface of the heater plate andopposed surfaces of the upper and lower plates, the edge sealcomprising: an elastomeric band having an outer concave surface in anuncompressed state, the band dimensioned to fit in the groove such thatan inner periphery of the band surrounds the heater plate and the upperand lower bond layers and upper and lower ends of the band are axiallycompressed between the upper and lower plates such that a maximumoutward bulging of the band is no greater than a predetermined distance14. The edge seal of claim 13, wherein the concave surface is a singlecurved surface, a single inclined surface such that the band is widestat an upper end thereof and narrowest at a lower end thereof or a pairof converging surfaces which form an obtuse angle such that the band iswidest at upper and lower ends thereof and narrowest at a middlethereof.
 15. The edge seal of claim 13, wherein the outer surface of theband includes a cylindrical surface of uniform diameter at an upper endof the band extending less than 1/10 of the height of the band.
 16. Theedge seal of claim 13, wherein the band has a height of 0.05 to 0.15inch, a width of 0.025 to 0.050 inch, and inner diameter of 11.3 to 11.4inches and each edge of the band is rounded with a radius of 0.001 to0.010 inch.
 17. The edge seal of claim 13, wherein the band has an upperannular surface, a lower annular surface smaller in width than the upperannular surface, a cylindrical inner surface of uniform diameterextending between the upper and lower annular surfaces, an outercylindrical surface of uniform diameter extending about 0.01 inch fromthe upper annular surface and a curved surface of uniform radiusextending between the outer cylindrical surface and the lower annularsurface.
 18. The edge seal of claim 13, wherein the predetermineddistance is no greater than 0.004 inch.
 19. The edge seal of claim 13,wherein the band includes a cylindrical inner surface of uniformdiameter, flat upper and lower surfaces of equal width, an outer curvedsurface extending between the upper and lower surfaces, and each edge ofthe band is rounded.
 20. The edge seal of claim 13, wherein the edgeseal is made of perfluoroelastomer material having a Shore Hardness A of60 to 75 and a specific gravity of 1.9 to 2.1.
 21. The edge seal ofclaim 13, wherein the edge seal has a cross-sectional aspect ratio ofheight:thickness of 2 to
 5. 22. The edge seal of claim 13, wherein theedge seal has a cylindrical inner surface with one or more geometricalfeatures thereon.
 23. The edge seal of claim 22, wherein the one or moregeometrical features comprise at least one depression in the innersurface or projection on the inner surface.